Most conventional manually driven wheelchair assemblies are directed toward paraplegic persons having full or partial use of both hands. Triplegic or monobrachius persons having use of only a single hand (i.e., one-handed persons), however, cannot manually operate these assemblies. Modifications to the drive wheels are generally required which allow manual operation of both wheels from the working-hand side of the wheelchair.
Ordinarily, single-handed drive assemblies for manual wheelchairs provide two individually operable and concentrically positioned manual hand-rim assemblies, each driving one wheel, which are mounted on the working-hand side of the wheelchair frame. A first hand-rim assembly is directly mounted to the rim of a first wheel on one side of the wheelchair, while the second hand-rim assembly, located adjacent to and concentric with the first hand-rim assembly, is operably coupled to an opposite second wheel positioned on an opposing side of the wheelchair frame. An elongated drive axle operably couples the central hub of the second wheel to the second hand-rim assembly. Typically, the drive axle extends coaxially with the central hub of the first wheel and is rotationally independent thereof. Accordingly, the second hand-rim assembly is operably coupled to the second drive wheel in a manner enabling the second drive wheel to be driven by manual rotation of the second hand-rim assembly, which is positioned adjacent to the first hand-rim assembly of the working hand side on the wheelchair.
While these prior art single-handed manual drive wheelchair configurations have successfully provided one-handed persons with a means for operating a manual wheelchair, such wheelchairs often present transportation or portability problems in vehicles. Two-handed manually operated wheelchairs, for example, often include wheelchair frames which are collapsible, that is, the side frames are mounted to scissor-like cross frame members such that the opposing sides of the frame can be repositioned into close proximity to one another. Hence, the overall dimension of standard two-handed manual wheelchairs can be substantially reduced, which facilitates portability, storability and transportability in vehicles. Most transport vehicles, accordingly, will not require any special modifications to carry these manual wheelchairs when the frame is collapsed.
Providing collapsible frames for one-handed manual drive wheelchairs, however, is much more difficult and problematic to achieve. As above-indicated, the rigid drive axle usually extends transverse to the sides of the wheelchair frame in an orientation essentially parallel to the direction of the collapse of the conventional collapsing frame. Accordingly, without significant alteration, the drive axle substantially opposes this collapse.
One attempt to overcome this problem includes providing a pivotal joint or series of pivotal joints along the drive axle which allows the drive axle to fold in discrete sections. These sections pivot about a joint axis or axes which is/are oriented perpendicular to the longitudinal axis of the drive axle. Hence, during collapse of the wheelchair frame from the deployed position to a collapsed position, the drive axle similarly moves from an extended position, where each axle section is coaxial with the longitudinal drive axis of the drive axle, to a collapsed position, where the discrete sections of the drive axle pivot about the joints in a manner away from axial alignment.
Pivotally jointed drive axles, however, have several disadvantages. For instance, the drive axle may have to be rotated to a specific orientation to properly align the joint axes so that the axle segments can correctly pivotally fold before the wheelchair frame can be collapsed. These two maneuvers (i.e., aligning the joints of the drive axle and collapsing the wheelchair frame) may be extremely difficult for one-handed persons to simultaneously coordinate. Moreover, these jointed drive axles cause substantial backlash between the hand-rim assembly and the connected drive wheel as the pivotal joints tend to loosen with time and wear. This results in poor response of the connected second drive wheel upon initial manual rotation of the hand-rim assembly. When the operator grips both hand-rim assemblies at the same time to move the chair forward, the first drive wheel will be initially responsive while the second drive wheel, coupled to the drive axle, will not. Hence, the wheelchair operator has start-up problems driving the wheelchair in the desired direction.